Characteristics of referred muscle pain to the head from ... · trigger points in women with...

ORIGINAL

Characteristics of referred muscle pain to the head from activetrigger points in women with myofascial temporomandibularpain and fibromyalgia syndrome

Cristina Alonso-Blanco • Cesar Fernandez-de-las-Penas •

Ana Isabel de-la-Llave-Rincon • Pedro Zarco-Moreno •

Fernando Galan-del-Rıo • Peter Svensson

Received: 21 July 2012 / Accepted: 18 August 2012 / Published online: 31 August 2012

� The Author(s) 2012. This article is published with open access at Springerlink.com

Abstract Our aim was to compare the differences in the

prevalence and the anatomical localization of referred pain

areas of active trigger points (TrPs) between women with

myofascial temporomandibular disorder (TMD) or fibro-

myalgia (FMS). Twenty women (age 46 ± 8 years) with

TMD and 20 (age 48 ± 6 years) with FMS were recruited

from specialized clinic. Bilateral temporalis, masseter, ster-

nocleidomastoid, upper trapezius, and suboccipital muscles

were examined for TrPs. TrPs were identified by palpation

and considered active when the pain reproduced familiar

pain symptom experienced by the patient. The referred pain

areas were drawn on anatomical maps, digitalized and also

measured. A new analysis technique based on a center of

gravity (COG) method was used to quantitative estimate of

the localization of the TrP referred pain areas. Women with

FMS exhibited larger areas of usual pain symptoms than

women with myofascial TMD (P \ 0.001). The COG

coordinates of the usual pain on the frontal and posterior

pain maps were located more superior in TMD than in FMS.

The number of active TrPs was significantly higher in TMD

(mean ± SD 6 ± 1) than in FMS (4 ± 1) (P = 0.002).

Women with TMD exhibited more active TrPs in the tem-

poralis and masseter muscles than FMS (P \ 0.01). Women

with FMS had larger referred pain areas than those with

TMD for sternocleidomastoid and suboccipital muscles

(P \ 0.001). Significant differences within COG coordinates

of TrP referred pain areas were found in TMD, the referred

pain was more pronounced in the orofacial region, whereas

the referred pain in FMS was more pronounced in the cer-

vical spine. This study showed that the referred pain elicited

from active TrPs shared similar patterns as usual pain

symptoms in women with TMD or FMS, but that distinct

differences in TrP prevalence and location of the referred

pain areas could be observed. Differences in location of

referred pain areas may help clinicians to determine the most

relevant TrPs for each pain syndrome in spite of overlaps in

pain areas.

Keywords Temporomandibular disorders � Fibromyalgia �Trigger points � Referred pain � Pain assessment

C. Alonso-Blanco

Department of Nursing, Universidad Rey Juan Carlos,

Alcorcon, Madrid, Spain

C. Fernandez-de-las-Penas � A. I. de-la-Llave-Rincon �F. Galan-del-Rıo

Department of Physical Therapy, Occupational Therapy,

Rehabilitation and Physical Medicine, Universidad Rey

Juan Carlos, Alcorcon, Madrid, Spain

C. Fernandez-de-las-Penas � A. I. de-la-Llave-Rincon �F. Galan-del-Rıo

Esthesiology Laboratory of Universidad

Rey Juan Carlos, Alcorcon, Spain

C. Fernandez-de-las-Penas (&)

Facultad de Ciencias de la Salud, Universidad Rey Juan Carlos,

Avenida de Atenas s/n, 28922 Alcorcon, Madrid, Spain

e-mail: [email protected]; [email protected]

P. Zarco-Moreno

Department of Rheumatology,

Fundacion Hospital Alcorcon, Alcorcon, Spain

P. Svensson

Department of Clinical Oral Physiology, School of Dentistry,

University of Aarhus, Aarhus, Denmark

P. Svensson

Department of Oral and Maxillofacial Surgery,

Aarhus University Hospital, Aarhus, Denmark

P. Svensson

Orofacial Pain Laboratory, Center for Sensory-Motor

Interaction, Aalborg University, Aalborg, Denmark

123

J Headache Pain (2012) 13:625–637

DOI 10.1007/s10194-012-0477-y

Introduction

Temporomandibular (TMD) pain is a musculoskeletal local

pain condition with a prevalence rate between 3 and 15 %,

an incidence rate between 2 and 4 % [1] and a women–men

ratio 2:1 [2]. Similar, fibromyalgia (FMS) is a widespread

diffuse musculoskeletal pain condition with a prevalence

ranging from 0.5 % to 5.0 and a higher proportion of

women [3, 4]. Although the etiology and pathology

of TMD and FMS are under debate, there is evidence of

facilitated nociceptive processes in both conditions. In fact,

TMD pain has been frequently diagnosed on fibromyalgia

subjects [5, 6] whereas the presence of widespread pain has

been shown to be a significant risk factor for myofascial

TMD [7]. A recent study has found an increased risk for the

onset of clinically significant TMD pain when subjects also

had FMS [8]. Therefore, it seems that TMD and FMS may

share some patho-physiological mechanisms.

In the last years, there has been an increasing interest for

the role of myofascial trigger points (TrPs) in both TMD [9]

and FMS [10]. TrPs are defined as hypersensitive spots

within a taut band of a skeletal muscle that are painful on

stimulation and give rise to a referred distant pain [11].

Active TrPs are spots with local and referred pain that

reproduce the clinical pain symptom experienced by the

patient and associated with the usual pain reported by the

patient. Latent TrPs have similar clinical findings as active

TrPs, but, in contrast, they do not mimic the painful symp-

toms [11]. Clinical distinction between active and latent TrPs

is substantiated by histo-chemical findings because higher

levels of neuroactive mediators (i.e., bradykinin, substance

P, or serotonin) have been found in active TrPs compared

with latent TrPs and non-TrP [12, 13].

Two recent studies have demonstrated that referred pain

from TrPs in the head and neck muscles reproduced

symptoms in women with myofascial TMD [14] or FMS

[15]. Nevertheless, these previous studies did not provide a

quantitative estimation of the localization of referred pain

areas. Two previous studies have used a new analysis

technique based on a centre of gravity (COG) method to

estimate the localization of the referred pain areas elicited

by injection of hypertonic saline into head and neck mus-

cles in healthy subjects [16, 17]. With this technique it

would be possible to estimate the anatomical localization

of the referred pain elicited by active TrPs in pain popu-

lations. Previous studies demonstrated that FMS is highly

co-morbid with primary headaches such as tension-type

and migraine headaches [18, 19] and TMD [5–7]. The

identification and quantification of differences in TrP dis-

tribution and location of the referred pain between patients

with TMD or FMS could be helpful for better clinical

identification of pain patterns in these populations in spite

of overlaps in symptomatology and clinical presentation of

pain. In addition, identification of those muscles most

affected by TrP in each group of patients could possibly

also be helpful for better management of TrP in these

populations. Application of the COG technique with

quantification of overlapping pain patterns in the head

could therefore be an important novel feature in a more

standardized description of patients with TMD and FMS.

To the best of the authors’ knowledge, no previous study

has investigated the differences in the prevalence of active

muscle TrPs and the anatomical localization of the referred

pain areas between patients with TMD and FMS. There-

fore, the aims of the current study were to compare the

differences in the prevalence and the anatomical localization

of referred pain areas of active TrPs in head and neck–

shoulder musculature between women with strict myofascial

TMD and FMS.

Methods

Participants

In the current study, women with a main diagnosis of FMS

or myofascial TMD were included. Participants were

recruited among patients referred from a tertiary special-

ized clinic on chronic pain in Madrid, Spain. They were

carefully screened and explored to further determine the

inclusion and exclusion criteria by an experienced dentist

(TMD group) or rheumatologist (FMS group). All patients

had prior to the referral received treatment but without

adequate pain relief, i.e., they represented, at least in part, a

treatment resistant proportion of myofascial TMD and

FMS patients.

To be included in the TMD group, women should fulfill

a primary and exclusive diagnosis of myofascial TMD

according to the Research Diagnostic Criteria for TMD

(RDC/TMD) [20]. Pain location, range of jaw motion,

temporomandibular joint (TMJ) pain, clicking sounds,

crepitation, and pain upon palpation of muscles and TMJ

were assessed with the use of the RDC/TMD criteria. Pain

should be presented with duration of at least 3 months and

an intensity of at least 3 on an 11-point numerical pain

rating scale (NPRS; 0: no pain; 10: maximum pain). Sub-

jects were excluded if they exhibited any of the following:

1, signs or symptoms according to categories II-III of the

RDC-TMD criteria (disc displacement, arthralgia, osteo-

arthrosis or osteoarthritis); 2, TMJ surgery or steroid

injections; 3, comorbid fibromyalgia; 4, diagnosis of any

systemic disease (rheumatoid arthritis, systemic lupus

erythematosis, psoriatic arthritis); 5, previous cervical or

head trauma; 6, presence of a score[8 points in the BDI-II;

7, diagnosis of primary headache (tension-type headache or

migraine); or, 8, cognitive impairment.

626 J Headache Pain (2012) 13:625–637

123

To be included within the FMS group, women should

fulfil the criteria from the American College of Rheuma-

tology (ACR) [21]. Tender points were tested by digital

palpation at the nine paired sites according to the ACR by

an experienced rheumatologist. The presence of wide-

spread pain, fatigue and altered sleep was also recorded. In

this group, the presence of TMD symptoms was not con-

sidered as exclusion criteria. Subjects were excluded if

presented any of the following: 1, severe physical dis-

ability; 2, comorbid conditions (inflammatory disease,

irritable bowel syndrome, interstitial cystitis); 3, uncon-

trolled endocrine disorders (hypo-thyroidism, diabetes); 4,

diagnosis of primary headaches (tension-type headache or

migraine); 5, malignancy; 6, psychiatric illnesses (schizo-

phrenia or substance abuse); 7, medication usage other than

as-needed analgesics (excluding long-term narcotics); 8,

history of surgery; 9, previous history of whiplash injury;

10, presence of a score [8 points in the BDI-II; or, 11,

cognitive impairment.

The study protocol was approved by local Ethics

Committee (URJC 08-30) and conducted following the

Helsinki Declaration. All participants signed informed

consent prior to their inclusion.

Self-reported measures

A numerical pain rate scale (NPRS) was used to assess the

usual level of pain, worst and lowest level of pain expe-

rienced in the preceding week at rest in the orofacial area

[22]. In the present study, the usual level of pain was

related to pain experienced normally by the patient, and not

the pain level on the day of examination. Women with

FMS were asked to focus the pain assessment on the oro-

facial region. They were also asked to draw the distribution

of their usual pain pattern within an anatomical map

including lateral, frontal, and occipital projections of the

face (dimensions 65 9 80 mm, Fig. 1).

The Beck Depression Inventory (BDI-II) a 21-item self-

report measure assessing affective, cognitive and somatic

symptoms of depression, was used to exclude patients with

depressive symptoms (BDI-II [8 points) [23]. The BDI-II

has shown good internal consistency (a = 0.86) with higher

scores indicating higher levels of depression [24, 25].

Muscle trigger point (TrP) examination

Trigger points were bilaterally explored within the tem-

poralis, masseter, upper trapezius, sternocleidomastoid and

suboccipital muscles by an examiner with more than

10 years’ experience in muscle TrP examination. TrP

diagnosis was done following the criteria as described by

Simons et al. [11]: 1, presence of a palpable taut band in a

skeletal muscle; 2, presence of a sensitive spot within the

taut band; 3, local twitch response elicited by the snapping

palpation of the taut band; and 4, presence of referred pain

in response to TrP compression (approximately 20 N force

for 5 s). Gerwin et al. [26] found that these criteria, when

applied by an experienced examiner, have good inter-

examiner reliability (kappa) ranging from 0.84 to 0.88.

Trigger point diagnosis within the suboccipital muscles

was made when there was local tenderness in the suboc-

cipital region, referred pain with maintained pressure for

10 s and increased referred pain with active extension of

the upper cervical spine [27].

Trigger points were considered active when both the

local and the referred pain evoked by the compression

reproduced the usual pain symptoms, and the elicited pain

was familiar for the participant [11]. For that purpose, after

TrP assessment on each muscle, subjects were asked:

‘‘When I pressed this muscle, did you feel pain or dis-

comfort locally, and in another area (referred pain). If yes,

please tell me whether the pain that you felt in the other

area reproduced the pain that you normally experience.’’

The order of muscle TrP evaluation was randomized

Fig. 1 Schematic presentation of the center-of-gravity (COG) technique. The X and Y coordinates of the COG were calculated in a 13 9 16 grid

system (see ‘‘Methods’’)

J Headache Pain (2012) 13:625–637 627

123

between participants. As both groups have pain symptoms,

TrP assessment was conducted in a blinded fashion in

relation to specific diagnosis.

Assessment of referred pain area and center of gravity

(COG)

Local pain was defined as pain located around the com-

pression site, and referred pain was defined as the pain

located at least 1 cm outside the local pain area evoked by

TrP palpation. Participants were asked to draw the distri-

bution of the referred pain after palpation of each muscle

TrP on the same anatomical map including lateral, frontal,

and occipital projections of the face/neck (dimensions:

65 9 80 mm). Specific information on possible referral

patterns was avoided in order not to induce bias [28]. The

usual pain area and the TrPs referred pain areas were

measured with a digitizer (ACECAD, model D9000 ?

digitizer, Taiwan) to calculate the area of perceived pain

expressed in arbitrary units (au).

To obtain a quantitative estimate of the localization of

the perceived pain areas, usual pain symptoms or referred

pain areas elicited by active TrPs, the centre-of-gravity

(COG) was calculated according to previous studies [16,

17]: a grid outline with 5-mm resolutions (i.e., a total of

13 9 16 = 208 grids) was superimposed on lateral, frontal

and occipital pain maps (Fig. 1). Each grid in the coordi-

nate system was assigned a value on a dichotomous basis

(0: no pain, 1: pain). The COG coordinates (X anterior–

posterior, Y inferior–superior) in arbitrary units (au) were

calculated according to the following formula:

x ¼X13

i¼0

X16

j¼0

xi � grid valuei;j

� �=X13

i¼0

X16

j¼0

grid valuei;j

y ¼X13

i¼0

X16

j¼0

yi � grid valuei;j

� �=X13

i¼0

X16

j¼0

grid valuei;j

Statistical analysis

Results are expressed as means, standard deviations (SD)

and 95 % confidence intervals (95 % CI). The Kolmogorov–

Smirnov test revealed a normal distribution of all quanti-

tative variables (P [ 0.05). Differences in pain parameters

between groups were assessed with the unpaired Student’s

t test. The Chi square (v2) test was used to assess the dif-

ferences in the distribution of TrPs for each muscle on

either side within both groups. A two-way analysis of

variance (ANOVA) with area (frontal, non-dominant

dominant, posterior) as within-subjects variable and group

(TMD, FMS) as the between-subjects variable was used to

assess differences in usual symptomatic pain areas between

groups. Differences in X and Y coordinates of usual pain

areas between groups were assessed with the unpaired

Student’s t test. Differences in the number of active TrPs

between groups were assessed with the non-parametric

Mann–Whitney U test. A three-way analysis of variance

(ANOVA) was used to compare referred pain areas (au)

between sides (dominant/non dominant) and muscles (i.e.,

temporalis, masseter, upper trapezius, and sternocleido-

mastoid) as within-subjects factors and group (TMD, FMS)

as between-subjects factor. A similar 2-way ANOVA was

used for the referred pain area from suboccipital muscles

without side as factor. The Bonferroni test was used for

post hoc analyses. Differences in X and Y coordinates of

TrPs referred pain areas between groups were assessed

with the unpaired Student’s t test. Finally, the Spearman’s

rho (rs) test was used to analyze the association between

the number of TrPs, the referred pain areas and pain

parameters. A P value \ 0.05 was considered statistically

significant.

Results

Demographic and clinical data of the sample

Table 1 summarizes clinical and demographic data of both

groups. Sixty-two (n = 62) consecutive patients with a

diagnosis of TMD (n = 30) or FMS (n = 32) were

screened for eligibility criteria. Ten (33 %) patients with

TMD [migraine (n = 4), fibromyalgia syndrome (n = 4),

previous whiplash (n = 2)] and 12 (37 %) with FMS [high

levels of depression (n = 7), previous whiplash (n = 5)]

were excluded. Finally, a total of 20 women with strict

myofascial TMD (mean age 46 ± 8 years) and 20 women

with FMS (age 48 ± 6 years) satisfied all the inclusion

criteria and agreed to participate.. Women with FMS exhib-

ited a longer duration of the pain condition (P \ 0.001), and

higher usual level of pain, worst and lowest level of pain

experienced in the preceding week at rest in the orofacial area

(P \ 0.001).

Usual pain areas in the orofacial region

Table 2 shows the mean values of X and Y coordinates of

the COG for women with myofascial TMD or FMS. The

mean usual pain area in women with myofascial TMD was

12.5 au (95 % CI 8.1–17.0) in the frontal region (n = 17,

85 %), 43.7 au (95 % CI 28.4–59.0) in the occipital region

and posterior part of the neck (n = 12, 60 %), 24.5 au

(95 % CI 17.3–31.7) on the dominant side of the head

(n = 14, 70 %), and 17.8 au (95 %CI 12.1–23.6) in the

non-dominant side of the face (n = 20, 100 %). Women

with FMS reported a usual pain area of 36.1 au (95 % CI

22.0–49.8) in the frontal area (n = 19, 95 %), 71.1 au

628 J Headache Pain (2012) 13:625–637

123

(95 % CI 46.3–95.9) in the occipital region and posterior

part of the neck (n = 20, 100 %), 34.3 au (95 % CI

25.1–43.6) on the dominant side of the head (n = 16,

80 %), and 27.2 au (95 % CI 18.5–36.4) on the non-

dominant side of the face (n = 15, 75 %).

The ANOVA indicated significant differences between

groups (F = 15.207; P \ 0.001) and regions (F = 12.005;

P \ 0.001) for usual pain symptoms. No significant group 9

region interaction was found (F = 1.005, P = 0.370). The

post hoc analysis revealed that women with FMS exhibited

larger pain areas of usual pain symptoms in the face than

women with myofascial TMD (P \ 0.01), and that the pain

area within the posterior region of the head was signifi-

cantly larger than the remaining pain areas (P \ 0.001). No

significant associations between the intensity or duration of

pain and usual pain areas in either group were found

(P [ 0.145).

In addition, significant differences between the location

of the Y coordinate on the frontal side (t = -2.190;

P = 0.045) and posterior region (t = -2.981; P = 0.006):

the pain areas in women with TMD were located more

superior (higher Y value) than in women with FMS. No

significant differences for the remaining coordinates of the

COG were found between groups (P [ 0.147, Fig. 2).

Prevalence of Muscle TrPs

Table 3 details the distribution of TrPs in both women with

myofascial TMD or FMS. The mean ± SD number of

active TrPs in women with myofascial TMD was 6 ± 1

and 4 ± 1 in women with FMS (z = -3.105; P = 0.002).

A significant association between the number of active

TrPs and usual pain (rs = 0.492; P = 0.027) was found in

TMD, but not in FMS (rs = 0.027; P = 0.909). No other

association between the number of active TrPs and the

other pain parameters was found.

The distribution of active muscle TrPs between women

with myofascial TMD or FMS was significantly different for

both temporalis (right: v2 = 18.649, P \ 0.001; left: v2 =

26.471, P \ 0.001), left masseter (v2 = 6.154, P = 0.046),

left upper trapezius (v2 = 10.326, P = 0.006), and both

sternocleidomastoid (right: v2 = 21.073, P \ 0.001; left:

v2 = 12.939, P = 0.002) muscles: women with myofascial

TMD exhibited a greater number of active TrPs in these

muscles as compared to women with FMS.

No significant differences in the distribution of right

masseter (v2 = 4.732, P = 0.984), right upper trapezius

(v2 = 5.700, P = 0.058), and suboccipital (v2 = 4.637,

P = 0.098) muscles were found between groups.

TrP referred pain areas

Table 4 summarizes size of the referred pain areas in all

muscles in women with myofascial TMD or FMS. A three-

way ANOVA revealed significant differences in referred

pain areas between muscles (F = 24.002, P \ 0.001), but

not between groups (F = 3.023, P = 0.083) or sides

(F = 0.084, P = 0.772). A significant interaction between

Table 1 Clinical pain parameters between women with myofascial TMD (n = 20) or FMS (n = 20)

Myofascial TMD FMS Significance

Pain history (years) 2.3 ± 1.3 (1.7–2.9) 6.7 ± 2.3 (5.6 –7.8) z = -5.003; P \ 0.001

Usual level of pain (0–10) 4.1 ± 1.3 (3.5–4.8) 6.0 ± 1.0 (5.5–6.4) z = -3.812; P \ 0.001

Worst level of pain (0–10) 6.5 ± 0.9 (6.0–6.9) 8.4 ± 0.8 (8.0–8.8) z = -4.787; P \ 0.001

Lowest levels of pain (0–10) 1.9 ± 0.8 (1.6–2.4) 3.8 ± 1.0 (3.3–4.3) z = -4.538; P \ 0.001

Data are expressed as mean ± SD (95 % confidence interval)

TMD temporomandibular disorder, FMS fibromyalgia syndrome, NPRS numerical pain rate scale

Table 2 Center-of-gravity (COG) measurements of usual pain drawing in the orofacial region in women with myofascial TMD or with FMS

[mean ± SD (95 % CI)]

Frontal projection Posterior projection Dominant (right) side Non-dominant (left) side

X Y* X Y* X Y X Y

TMD 7.4 ± 1.2

(6.7–7.2)

10.4 ± 2.3

(12.5–13.5)

6.9 ± 0.4

(6.8–7.0)

7.1 ± 2.3

(5.7–7.6)

7.3 ± 1.2

(7.4–8.9)

9.5 ± 2.0

(12.0–14.0)

7.3 ± 1.6

(7.5–8.2)

8.7 ± 1.8

(11.8–13.4)

FMS 6.8 ± 0.7

(6.4–7.0)

12.1 ± 2.9

(13.5–14.0)

7.1 ± 0.2

(7.0–7.1)

5.3 ± 1.2

(6.2–10.5)

7.4 ± 1.1

(6.0–8.0)

11.3 ± 3.4

(11.5–14.6)

7.4 ± 2.1

(6.9–8.5)

8.9 ± 4.4

(12.4–14.0)

TMD temporomandibular disorder, FMS fibromyalgia syndrome

* Significant differences between TMD and FMS (Student’s t test, P \ 0.05)

J Headache Pain (2012) 13:625–637 629

123

group 9 muscle (F = 4.601, P = 0.004), but not for

group 9 side (F = 0.009, P = 0.926), side 9 muscle

(F = 0.030, P = 0.993) or group 9 muscle 9 side (F =

0.061, P = 0.980) was found.

The two-way ANOVA for the suboccipital muscles

revealed significant differences between group (F =

30.646, P \ 0.001) and muscle (F = 17.391, P \ 0.001)

and an interaction between group 9 muscle (F = 15.438,

P \ 0.001). The Bonferroni analyses showed that women

with FMS exhibited larger referred pain areas than those

with myofascial TMD for sternocleidomastoid and suboc-

cipital muscles (P \ 0.001), but not for the temporalis,

masseter or upper trapezius (P [ 0.763). The referred pain

area elicited by suboccipital TrPs was significantly larger

than the referred pain elicited from the remaining muscles

(P \ 0.001) within the FMS, but smaller within the TMD

(P \ 0.01). Further, the referred pain area from upper

trapezius TrPs was significantly larger than the referred

Fig. 2 Center-of-gravity (COG) and areas of the usual pain symptoms in women with TMD (top) or with FMS (bottom). The length of the pain

vector (arrow) is computed in arbitrary units

Table 3 Number of women with myofascial temporomandibular disorder or with fibromyalgia with active muscle trigger points (TrPs) in head

and neck–shoulder muscles

Temporalis* Masseter Upper trapezius Sternocleidomastoid* Suboccipital

Right Left Right Left* Right Left* Right Left Bilateral

Myofascial Temporomandibular disorders (n = 20)

Active TrPs (n) 12 16 12 16 12 16 8 11 14

No TrPs (n) 8 4 8 4 8 4 12 9 6

Fibromyalgia syndrome (n = 20)

Active TrPs (n) 5 1 14 10 18 11 3 5 13

No TrPs (n) 15 19 6 10 2 9 17 15 7

* Significant differences between TMD and FMS (Chi square, P \ 0.05)

630 J Headache Pain (2012) 13:625–637

123

pain areas elicited by temporalis, masseter and sternoclei-

domastoid muscle TrPs in both groups (P \ 0.001).

Table 5 summarizes mean values of X and Y coordinates

of the COG of referred pain areas from TrPs for women

with TMD or TMD. Significant differences between

Y coordinates within the temporalis (t = -2.929, P =

0.008) and masseter (t = -2.921, P = 0.007) muscles of

the right (dominant) side were found: the TrP referred pain

area in women with TMD (Fig. 3) was located more

inferior (lower Y values) than in women with FMS (Fig. 4).

Significant differences were also found within the upper

trapezius muscle for X coordinates of the posterior area

(t = -2.320, P = 0.027) and X (t = -2.015, P = 0.048)

and Y (t = -2.243, P = 0.035) coordinates on the left

(non-dominant) side: TrP referred pain area in the posterior

part of the head was located more medially (greater

X value) in women with FMS (Fig. 4) than in women with

TMD (Fig. 3), whereas the referred pain area of the left

upper trapezius was located more medially (greater

X value) and superior (greater Y value) in women with

TMD. Finally, referred pain areas from suboccipital muscle

TrPs were more superior (greater Y value) bilaterally

(t = -2.407, P = 0.037) in women with TMD (Fig. 3)

than in those with FMS (Fig. 4).

Discussion

This study revealed that the referred pain elicited from

active TrPs in head and neck–shoulder musculature

reproduced the pain pattern in the orofacial region in

women with myofascial TMD or FMS. In addition, dif-

ferences in TrP prevalence and spreading of the referred

pain areas were observed as women with myofascial TMD

exhibited more active TrPs than women with FMS,

whereas women with FMS exhibited larger referred pain

areas for sternocleidomastoid and suboccipital muscles.

Furthermore, the referred pain areas of temporalis and

masseter muscle TrPs were located more inferior (within

the orofacial area) in women with TMD, whereas upper

trapezius TrP referred pain was located more inferior

(located in the neck area) in women with FMS.

The relationship between orofacial pain and FMS has

been previously reported as it is commonly seen that

women with FMS also exhibit symptoms in this area [5, 6].

In the current study, we found that women with FMS

exhibited a longer duration of the painful condition and

higher levels of pain in the orofacial area than those with

myofascial TMD, which is to be expected as FMS is a

chronic condition with longer period before the diagnosis.

Another difference was that usual pain within the frontal

and occipital areas was more superior (higher Y value) in

women with TMD than in women with FMS. Further,

women with FMS exhibited larger areas of usual pain than

women with TMD, which is expected as FMS is charac-

terized by a greater impairment of nociceptive pathways

[8]. The present findings reveal that the location of usual

pain symptoms in the orofacial region is similar between

women with pure myofascial TMD and FMS, but the pain

is more widespread in FMS.

The presence of active TrP referred pain in myofascial

TMD or FMS corroborates previous studies, which have

demonstrated the relevance of active muscle TrPs in

women with myofascial TMD [14] or FMS [15, 29] as

compared to healthy controls. In the current study, TrPs in

the masticatory muscles, temporalis and masseter, were

more prevalent than TrPs in neck muscles, sternocleido-

mastoid and suboccipital, in the TMD group whereas the

Table 4 Referred pain areas

(au) of active trigger points

(TrPs) in head and

neck–shoulder muscles in

women with myofascial

temporomandibular disorder or

with fibromyalgia

* Significant interaction

between group 9 muscle

(3-way ANOVA test, P \ 0.01)

Myofascial temporomandibular disorder Fibromyalgia syndrome

Temporalis

Right side (n = 12) 20.8 ± 10.8 (14.6–27.2) Right side (n = 5) 19.1 ± 8.5 (12.4–25.7)

Left side (n = 16) 21.2 ± 11.2 (14.5–27.9) Left side (n = 1) 19.3 ± 9.9 (12.8–25.8)

Masseter



Upper trapezius



Sternocleidomastoid*



Suboccipital*

Bilateral (n = 14) 7.6 ± 3.4 (5.8–11.1) Bilateral (n = 13) 49.6 ± 29.1 (38.6–60.6)

J Headache Pain (2012) 13:625–637 631

123

opposite was found in women with FMS. Our findings are

in contrast with data from tension-type headache where

TrPs in the cervical muscles were the most prevalent

[30–32]. It is expected that masticatory muscle TrPs play a

more relevant role in orofacial pain, whereas neck and

shoulder TrPs could play a greater role in headaches. In

fact, TrPs in the neck muscles were more prevalent than in

the masticatory muscles in women with FMS, possibly

reflecting clinical differences in muscle pain generators

between women with TMD or FMS. This distinction has

potential important clinical implications as it has been

suggested that regional pain in FMS, in this case orofacial

pain, can be caused by local active TrPs and/or referred

from remote active TrPs. A previous study showed that the

overall usual FMS pain is not simply diffuse body pain but

is located to certain body areas [33] supporting this

hypothesis. Therefore, the current study supports the

hypothesis that pain generators in different muscles can be

involved in orofacial pain (TMD), neck pain associated to

FMS and tension-type headache. Nevertheless, clinicians

should be aware that treatment of TMD and FMS may vary

but could in some patients include TrP therapy. In fact,

recent studies have supported the clinical relevance of TrPs

in both TMD [14] and FMS [15] related pain. It is possible

that a proper therapeutic approach targeted to specific TrPs

in the muscles identified by the described COG technique

in the current study may improve clinical outcomes in these

populations. Further studies are, however, needed to establish

the efficacy of TrP therapy in TMD and FMS.

In addition, clinical differences between TMD and FMS

were also present in the location of referred pain areas as

temporalis and masseter TrPs referred pain to the head

(more superiorly) in FMS but to the face (more inferiorly)

in TMD. In addition, suboccipital TrPs referred pain was

also more superiorly located in the head in TMD than in

FMS (neck). Therefore, it seems that TrP referred pain in

FMs is mostly located in the neck region, whereas TrP

referred pain in TMD is mostly located in the face area.

One possible patho-physiological mechanism explaining

differences in the location of the TrP referred pain can

be related to a different clinical manifestation or degrees

of trigeminal brain stem sensory nuclear complex

Table 5 Center-of-gravity (COG) measurements of referred pain drawing in women with myofascial temporomandibular disorder or with

fibromyalgia

Frontal projection Occipital projection Dominant (right) side Non-dominant (left) side

X Y X Y X Y X Y

Temporalis muscle

TMD NA NA NA NA 7.7 ± 1.1

(7.1–8.3)

11.5 ± 1.4*

(10.8–12.3)

7.6 ± 0.8

(7.2–8.0)

11.0 ± 1.4

(10.3–11.7)

FMS NA NA NA NA 7.2 ± 1.4

(5.8–8.6)

13.3 ± 0.5

(12.8–13.9)

6.1 ± 1.0

(5.7–9.9)

12.0 ± 1.4

(8.6–14.7)

Masseter muscle


(8.4–9.4)

7.9 ± 1.1*

(7.4–8.5)

9.0 ± 0.8

(8.6–9.4)

7.6 ± 1.2

(7.0–8.2)


(8.6–9.5)

9.4 ± 1.6

(8.5–10.3)

9.3 ± 0.8

(8.6–9.9)

8.3 ± 1.3

(7.3–9.4)

Upper trapezius muscle

TMD NA NA 6.6 ± 1.9*

(5.6–7.7)

4.1 ± 1.5

(3.3–4.9)

4.6 ± 1.1

(4.0–5.3)

5.6 ± 1.5

(4.8–6.4)

4.5 ± 1.1*

(3.8–5.2)

5.2 ± 1.7*

(4.3–6.2)

FMS NA NA 8.1 ± 1.6

(7.2–8.9)

4.4 ± 0.9

(3.8–4.9)

4.1 ± 0.4

(4.0–4.3)

5.8 ± 0.9

(5.4–6.3)

3.8 ± 0.4

(3.5–4.1)

3.9 ± 0.9

(3.3–4.6)

Sternocleidomastoid muscle


(6.6–7.5)

6.8 ± 1.9

(5.8–7.8)

7.2 ± 0.7

(6.8–7.5)

6.6 ± 2.0

(5.7–7.6)


(3.5–7.4)

8.6 ± 3.3

(6.3–12.9)

6.7 ± 1.3

(5.1–8.3)

8.3 ± 1.9

(5.9–10.8)

Suboccipital muscles

TMD 7.1 ± 0.4

(6.5–7.7)

13.7 ± 1.9

(10.7–16.7)

7.0 ± 0.5

(6.7–7.3)

8.9 ± 1.2

(8.3–9.6)

5.5 ± 2.5

(3.8–7.1)

10.4 ± 2.2*

(8.9–11.9)

5.3 ± 2.0

(4.0–5.7)

10.4 ± 2.2*

(9.1–11.8)

FMS 6.9 ± 0.1

(6.8–7.3)

13.3 ± 1.2

(12.1–14.6)

7.1 ± 0.3

(6.9–7.3)

9.7 ± 2.8

(7.6–11.8)

7.0 ± 0.3

(6.8–7.2)

16.1 ± 0.5

(16.0–16.5)

7.0 ± 0.7

(5.6–12.3)

14.5 ± 0.7

(8.1–18.8)

NA not applicable (there was no referred pain to this area of the head)

* Significant differences between women with myofascial TMD and FMS (Student’s t test, P \ 0.05)

632 J Headache Pain (2012) 13:625–637

123

Fig. 3 Center-of-gravity (COG) and areas of the referred pain elicited by active TrPs in women with myofascial TMD. The length of the pain

vector (arrow) is computed in arbitrary units

J Headache Pain (2012) 13:625–637 633

123

Fig. 4 Center-of-gravity (COG) and areas of the referred pain elicited by active TrPs in women with FMS. The length of the pain vector (arrow)

is computed in arbitrary units

634 J Headache Pain (2012) 13:625–637

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sensitization relative to cervical/spinal sensitization. It is

plausible that women with TMD would exhibit a greater

sensitization of the trigeminal neurons than women with

FMS which would explain the TrP referred pain location in

the face rather than in the neck for TrPs in the masticatory

muscles.

The presence of active TrPs indicates sensitization of

muscle nociceptors in both TMD and FMS since high

levels of neuroactive mediators [12, 13] and lower pressure

pain thresholds [34–37] have been found in active TrPs. In

fact, Hong [38–40] suggested the concept of multiple

sensitized nociceptors in the TrP region as the sensory units

responsible for the local twitch response when the TrP is

mechanically stimulated. Further, there is evidence dem-

onstrating that active TrPs may serve as potent peripheral

noxious input sensitizing central nervous system in FMS

and TMD. This hypothesis is supported by human experi-

mental studies showing that a single intramuscular anes-

thetic injection into the midpoint of the upper trapezius

muscle, a typical site of active TrPs in FMS patients, sig-

nificantly increased pain thresholds and decreases second-

ary heat hyperalgesia in FMS [41]. Therefore, studies

investigating the clinical relevance of TrPs inactivation in

the course of pain in the orofacial area in women with

myofascial TMD or FMS are clearly needed.

Finally, we should recognize some strengths and limi-

tations of the study. First, we included patients recruited

from tertiary clinics which may not represent the general

population. It is possible that patients seeking treatment in

specialized clinics exhibit different features and charac-

teristics than those recruited from a general population and

it is a common clinical observation that these patients

have inadequate pain relief from a variety of therapeutic

approaches (e.g., oral appliances, medication, etc.) [42]; so

direct extrapolations of the current results to the general

population should be avoided at this stage. In addition, our

sample size was relatively small. Therefore, future studies

with greater sample sizes and including patients recruited

from the general population are now needed to further

confirm the current results. Furthermore, FMS diagnosis is

a challenge for clinicians and researchers and new diag-

nostic criteria have been proposed [43]. Women with FMS

included in our study were diagnosed according to first

diagnostic criteria [21]. We do not know if the same results

would be found in women with FMS presenting the new

proposed criteria, but we speculate that there is a signifi-

cant concordance between the two sets of criteria. Second,

the TrP examination was conducted by a blinded examiner

ruling of the chance of bias. Nevertheless, it is possible that

a potential bias of patients’ recognition of the referred pain

may be present in TrP examination although this seems

unlikely. In addition, reproducibility of TrP diagnosis has

been questioned in recent reviews since studies of high

quality are needed [44, 45]. Factors that may have con-

tributed to the varying reliability of the results from pre-

vious studies are lack of identification of taut bands,

inexperience of the examiners in assessing TrPs or incor-

rect palpation techniques. Nevertheless, Gerwin et al. [26]

reported that TrP diagnosis has good inter-examiner reli-

ability when applied by an experienced examiner, as this

was conducted in this study. It should also be acknowl-

edged that the understanding of TrP remains incomplete

and further studies will be needed to clarify underlying

mechanisms as well as clinical manifestations. Third, we

included a specific group of women with strictly myofas-

cial TMD or with FMS. We excluded patients with other

concomitant RCD/TMD diagnosis and other co-morbid

conditions, i.e., primary headaches, with may be also

related to the presence of TrPs. Therefore, our results

should be considered with caution when extrapolate to

different groups of patient with FMS or TMD. Fourth, it is

suggested that psychological factors, e.g., anxiety and

depression, may enhance central nervous system responses

[46]. In the current study, we excluded a state of depression

in our patients with TMD or FMS ([8 points BDI-II).

Therefore, data are representative for women with myo-

fascial TMD pain or FMS without depression. Neverthe-

less, we do not know if anxiety, sleep disturbances, pain

catastrophizing etc. could also influence our results.

Finally, since we only included women, future studies

should investigate gender differences and determine if

similar results are present in men with TMD or FMS.

Conclusion

This study showed that the referred pain elicited from

active TrPs in head and neck–shoulder musculature

reproduced the pain pattern in the orofacial region in

women with myofascial TMD or FMS. Women with

myofascial TMD exhibited more active TrPs than women

with FMS, whereas women with FMS exhibited larger

referred pain areas for neck muscle TrPs. The referred pain

areas of temporalis and masseter muscle TrPs were located

more inferior (in the orofacial area) in TMD, whereas

upper trapezius TrP referred pain was located more inferior

(in the neck area) in FMS. The current study supports that

generators in different muscles can be involved in orofacial

pain (TMD) and neck–face pain associated to FMS.

Conflict of interest No conflict of interest has been declared by the

author(s).

Open Access This article is distributed under the terms of the

Creative Commons Attribution License which permits any use, dis-

tribution, and reproduction in any medium, provided the original

author(s) and the source are credited.

J Headache Pain (2012) 13:625–637 635

123

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